[swift-evolution] [Review] SE-0107: UnsafeRawPointer API (binding memory to type)

[Andrew Trick]

> On Jul 11, 2016, at 12:50 AM, Ben Rimmington <me at benrimmington.com> wrote:
> 
> 
>> On 10 Jul 2016, at 14:41, Andrew Trick via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> I'm revising this proposal based on last week's feedback. A few of the
>> additive APIs are removed and a number of UnsafePointer and
>> UnsafeRawPointer methods are renamed.
>> 
>> Here is a PR for the revision. Note that the examples in the proposal
>> text still need to be updated:
>> https://github.com/apple/swift-evolution/pull/420
>> 
>> I updated the short-form summary of the API:
>> https://github.com/atrick/swift-evolution/blob/3122ace9d2fb55072ebd7395c7353fcbf497318a/proposals/0107-unsaferawpointer.md#full-unsaferawpointer-api
>> 
>> The full UnsafeRawPointer API with doc comments is here:
>> https://github.com/atrick/swift/blob/22e3a2885e4236888ec447a7148acf633d8544f5/stdlib/public/core/UnsafeRawPointer.swift.gyb
>> 
>> The UnsafePointer and UnsafeRawPointer changes are on this branch:
>> https://github.com/atrick/swift/commits/rawptr
>> 
>> If you wish to comment line-by-line on the detailed docs or
>> implementation, you can do so here:
>> https://github.com/apple/swift/pull/3437
>> 
>> ---
>> The only concern I have about this version of the proposal is this method name: 
>> 
>>  func copyBytes(from: UnsafeRawPointer, count: Int)
>> 
>> because `count` usually refers to a number of values. I think it should be:
>> 
>>  func copy(bytes: Int, from: UnsafeRawPointer)
> 
> Using `bytes` to label the count / length / size would be inconsistent with:
> 
> 	Foundation.Data.init(bytes:count:)
> 	<https://developer.apple.com/reference/foundation/data/1780158-init>
> 
> 	Foundation.Data.copyBytes(to:count:)
> 	<https://developer.apple.com/reference/foundation/data/1780297-copybytes>
> 
> UnsafeMutableRawPointer could use a `size` or `sizeInBytes` label.
> (This also applies to the `allocate` and `deallocate` methods).
> 
> — Ben

Thanks for pointing that out.

My concern is code like:

  let ptrToInt: UnsafePointer<Int32> = …
  rawPtr.copyBytes(from: ptrToInt, count: 4)

which looks a lot like 4 Int32s will be copied when only 1 Int32 will actually be copied.

Anyone care to vote on this?

Current:

  let rawPtr = UnsafeMutableRawPointer.allocate(bytes: 24)
  rawPtr.copyBytes(from: ptrToInt, count: 24)
  rawPtr.deallocate(bytes: 24)

Proposed:

  let rawPtr = UnsafeMutableRawPointer.allocate(sizeInBytes: 24)
  rawPtr.copyBytes(from: ptrToInt, sizeInBytes: 24)
  rawPtr.deallocate(sizeInBytes: 24)

-Andy